Various shapes of induction motor rotor have been proposed by the use of double squirrel-cage shapes or the like for the purpose of improving locked-rotor torque, breakdown torque, and efficiency.
As an example, a rotor for a rotating electrical machine having a double squirrel-cage rotor core has been proposed (see e.g., Patent Document 1). The double squirrel-cage rotor core is formed to have intermediate bars fitted in slit portions that connect outside slots and inside slots. The intermediate bars are narrow near the outside slots and wide near the inside slots.    Patent Document 1: Unexamined Japanese Utility Model Publication No. SHO 62-68468